Integrated 3D microlenses for efficient light extraction from diamond quantum emitters using two-photon polymerization

Quantum emitters in solid-state hosts such as nitrogen-vacancy (NV) centers in diamond have emerged as a robust platform in various applications such as quantum computing, nanoscale metrology, and biological sensing. A high photon collection efficiency is a key requirement for all these applications. However, photon collection is severely hampered by the high refractive index of diamond (2.4) at visible wavelengths which traps photons by total internal reflection. Previously, this problem has been addressed by the fabrication of monolithic photonic structures such as solid-immersion and metalenses in diamond. However, these approaches are inherently complex, expensive, lack scalability, and are destructive. Here, we present a fast, scalable, and non-destructive process for the fabrication of polymer microlenses on a diamond substrate using two-photon polymerization. Using this process, we present the fabrication of hemispherical and hyperboloid three-dimensional micro-optical elements. The fidelity of fabricated structures is confirmed by scanning electron microscopy. The characterization is carried out using a custom-built confocal microscope. We demonstrate an enhancement in collected photoluminescence and an improvement in the acquisition speed of optically detected magnetic resonance (ODMR) from NV centers. These results open the possibility of using polymer micro-optical elements for scalable quantum applications.